Several publications are referenced in this application to more fully describe the state of the art to which this invention pertains. The disclosure of each such publication is incorporated by reference herein.
The control of gene expression in response to cell density, or quorum sensing, was first described in the marine luminous bacteria Vibrio fischeri and Vibrio harveyi. This phenomenon has recently become recognized as a general mechanism for gene regulation in many Gram negative bacteria. Quorum sensing bacteria synthesize, release, and respond to specific acyl-homoserine lactone signaling molecules called autoinducers to control gene expression as a function of cell density. In all acyl-homoserine lactone quorum sensing systems described to date, except that of V. harveyi, the autoinducer synthase is encoded by a gene homologous to luxI of V. fischeri, and response to the autoinducer is mediated by a transcriptional activator protein encoded by a gene homologous to luxR of V. fischeri (Bassler and Silverman, in Two component Signal Transduction, Hoch et al., eds, Am. Soc. Microbiol. Washington D.C., pp 431-435, 1995). In contrast, V. harveyi has two independent density sensing systems (called Signaling Systems 1 and 2), and each is composed of a sensor-autoinducer pair. V. harveyi Signaling System 1 is composed of Sensor 1 and autoinducer 1 (AI-1), and this autoinducer is N-(3-hydroxybutanoyl)-L-homoserine lactone (see Bassler et al., Mol. Microbiol. 9: 773-786, 1993). V. harveyi Signaling System 2 is composed of Sensor 2 and autoinducer 2 (AI-2) (Bassler et al., Mol. Microbiol. 13: 273-286, 1994). The structure of AI-2 heretofore has not been determined, nor have the gene(s) involved in biosynthesis of AI-2 been identified. Signaling System 1 is a highly specific system proposed to be used for intra-species communication and Signaling System 2 appears to be less species-selective, and is hypothesized to be for inter-species communication (Bassler et al., J. Bacteriol. 179: 4043-4045, 1997).
Reporter strains of V. harveyi have been constructed that are capable of producing light exclusively in response to AI-1 or to AI-2 (Bassler et al., 1993, supra; Bassler et al., 1994, supra). V. harveyi reporter strains have been used to demonstrate that a few species of bacteria produce stimulatory substances that mimic the action of AI-2 (Bassler et al., 1997, supra).
Quorum sensing in V. harveyi, mediated by Signaling Systems 1 and 2, triggers the organisms to bioluminesce at a certain cell density. These same signaling systems, particularly Signaling System 2, are believed to trigger other physiological changes in V. harveyi and other bacteria possessing the same signaling system. Thus, it would be an advance in the art to identify and characterize the signaling factor autoinducer-2 and the genes encoding the proteins required for its production. Such an advance would provide a means to identify a novel class of compounds useful for controlling mammalian enteric or pathogenic bacteria.